I have a GP Matt Chapman Cap 580. I've installed a Tower 75 with a Bison Pitts muffler for a GMS 76. After warm up, engine stalls at no particular time, idle, mid range, wide open throttle. I've tuned it many times. I have changed glow plugs, fuel tank, lines, ran it with and without the engine cowl. I have event tried another Tower 75 using the same Bison Pitts muffler. I suspicion it is overheating. Both these engines are broke in and have ran fine in other planes with there stock mufflers. I am using the same 15% Omega fuel that I broke these engines in on. The engine in this cap is mounted horizontal. Any body have any suggestions to correct this problem? I like the Tower 75 and the Cap 580. I would like to make it run in this plane before changing to another type of engine.